1. Field of the Invention
Apparatuses consistent with the present invention relate to an N×N multiple-input multiple-output (MIMO) transceiver, and more particularly, to an N×N MIMO transceiver capable of supplying a differential signal to plural transceivers by using one frequency synthesizer.
2. Description of the Related Art
With the spread of high-speed Internet, digital home networks are built in combination with high-speed internet networks such as digital subscriber line (DSL) and wireless local area networks, and, as high-capacity audio-visual (AV) multimedia services such as high definition class (HD-class) broadcasts increase, wireless communication technologies are required which have stable and high throughput such as throughput in excess of 100 Mbps.
Accordingly, the requirements of IEEE 802.11n, 16a/e, 20, and so on, which are the next-generation radio frequency (RF) standard have become more specific, and, in particular, it is necessary to develop a low-cost and low-power complementary metal oxide semiconductor (CMOS) RF solution to cope with the IEEE 802.11n.
To cope with such requirements, MIMO technologies have been proposed. The MIMO technologies are to connect plural transceivers each formed in one chip with a transmitter part and a receiver part, and the MIMO transceiver performs processing over plural signals so that the plural signals are transmitted through plural antennas at the same time, or processes plural signals input through individual antennas at the same time. Each receiver circuit included in the MIMO transceiver downconverts to baseband an RF signal input to a corresponding antenna thereof, and upconverts a baseband signal for transmissions to a corresponding antenna thereof.
The early MIMO transceiver used a pair of connected transceivers, which has no way to reduce the cost of the transceiver. Thus, there are proposed methods, some of which integrate a power amplifier into a transceiver or use one frequency synthesizer.
U.S. patent application Publication No. 2004/0121753, entitled “Multiple-Input Multiple-Output Radio Transceiver” discloses an MIMO transceiver using one frequency mixer. The frequency synthesizer includes voltage controlled oscillators (VCOs) and a phase locked loop (PLL). The VCO generates and supplies a differential signal of a certain frequency to the mixer, so that received data are down converted into a baseband frequency. Further, the PLL synchronizes a phase of a differential signal in order for the differential signal output from the VCO to stay at a certain phase angle.
However, such conventional methods and apparatuses can be designed to use one frequency synthesizer by applying a pair of receiver circuits and a pair of transmitter circuits to the MIMO transceiver of a 2×2 type, but the 4×4 to N×N MIMO transceivers, each having more than two pairs of receiver circuits and transmitter circuits, cannot employ a structure in which one frequency synthesizer is used.
Therefore, approaches are sought which cope with throughput requirements together with advancements of communications technologies, by applying one frequency synthesizer to the N×N MIMO transceiver.